The spokesman, Garad Salad, could not immediately say whether the explosion resulted in casualties.

But eyewitnesses said a security guard was killed while trying to fight off the bomber. The blast shattered windows of nearby buildings and left two others wounded, witnesses said.

No one claimed responsibility for the attack and it was unclear if Shirdon was in his office during the time of the attack.

Shirdon, an economist who used to run an import business in neighboring Kenya, was named prime minister in October.

When he accepted the position, Shirdon told the parliament that his government will do more to ensure the security of the country and to fight against terrorism and piracy.

Somalia plunged into chaos after dictator Mohamed Siad Barre was overthrown 21 years ago. Following his ouster, clan warlords and militants battled for control, sparking a civil war and mayhem nationwide.

The nation since then has mostly been under a shaky transitional federal government.